Image pickup apparatus, image pickup system, and image pickup apparatus driving method

ABSTRACT

Each of multiple pixels includes a photoelectric conversion unit. A first holding unit is configured to hold a charge generated by the photoelectric conversion unit, at a location different from location of the photoelectric conversion unit. A second holding unit is configured to hold a charge held by the first holding unit at a location different from locations of both of the first holding unit and the photoelectric conversion unit. An amplifying unit includes an input node different from the second holding unit and is configured to output a signal based on a charge transferred to the input node from the second holding unit. A first discharge unit includes a charge draining node which is electrically connected to a line where a predetermined voltage is supplied. The first discharge unit discharges a charge held by the first holding unit to the charge draining node.

BACKGROUND OF THE INVENTION

1. Field of the Invention

One disclosed aspect of the embodiments relates to an image pickupapparatus, an image pickup system, and an image pickup apparatus drivingmethod.

2. Description of the Related Art

In recent years, owing to further improvement in the performance ofimage pickup apparatuses, there has been studied a configurationincluding a charge holding unit within a pixel separately from aphotoelectric conversion unit and a floating diffusion (hereinafter,FD). As for usage of the holding unit, the holding unit is provided torealize a global electronic shutter as disclosed in Japanese PatentLaid-Open No. 2009-296574.

SUMMARY OF THE INVENTION

Some embodiments relate to an image pickup apparatus including aplurality of pixels. The plurality of pixels each include aphotoelectric conversion unit. The plurality of pixels each include afirst holding unit configured to hold a charge generated by thephotoelectric conversion unit, at a location different from thephotoelectric conversion unit. The plurality of pixels each include asecond holding unit configured to hold a charge held by the firstholding unit at a location different from both of the first holding unitand the photoelectric conversion unit. The plurality of pixels eachinclude an amplifying unit including an input node and configured tooutput a signal based on a charge transferred to the input node from thesecond holding unit. The input node is a different node from the secondholding unit. The plurality of pixels each include a first dischargeunit configured to discharge a charge of the first holding unit. Thefirst discharge unit includes a charge draining node. The chargedraining node is electrically connected to a line to which apredetermined voltage is to be supplied. The first discharge unit isconfigured to discharge a charge held by the first holding unit holds tothe charge draining node.

Some embodiments relate to a driving method of an image pickup apparatushaving a plurality of pixels. Each of the plurality of pixels includes afirst holding unit configured to hold a charge generated by aphotoelectric conversion unit, at a location different from thephotoelectric conversion unit, and a second holding unit configured tohold a charge held by the first holding unit at a location differentfrom both of the photoelectric conversion unit and the first holdingunit. The driving method according to the embodiments includes atransfer step to transfer a charge held by the first holding unit to thesecond holding unit. The driving method according to the embodimentsincludes a discharge step to discharge a charge of the first holdingunit via a path different from a charge transfer path of the transferstep.

Some embodiments relate to a driving method of an image pickup apparatushaving a plurality of pixels. Each of the plurality of pixels include afirst holding unit configured to hold a charge generated by aphotoelectric conversion unit, at a location different from thephotoelectric conversion unit, and a second holding unit configured tohold a charge held by the first holding unit at a location differentfrom both of the photoelectric conversion unit and the first holdingunit. The driving method according to the embodiments includes atransfer step to transfer a charge held by the first holding unit to thesecond holding unit. The driving method according to the embodimentsincludes a discharge step to discharge a charge of the first holdingunit. The discharge step is performed when the second holding unit holdsa charge.

Some embodiments relate to a driving method of an image pickup apparatushaving a plurality of pixels. Each of the plurality of pixels include afirst holding unit configured to hold a charge generated by aphotoelectric conversion unit, at a location different from thephotoelectric conversion unit, and a second holding unit configured tohold a charge held by the first holding unit at a location differentfrom both of the photoelectric conversion unit and the first holdingunit. The driving method according to the embodiments includes atransfer step to transfer a charge held by the first holding unit to thesecond holding unit. The transfer step is repeatedly executed. Thedriving method according to the embodiments includes a discharge step todischarge a part of charges held by the first holding unit in betweentwo consecutive executions of the transfer step.

Further features of the disclosure will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an embodiment of an image pickup apparatus.

FIG. 2 is a diagram illustrating an equivalent circuit of an embodimentof the image pickup apparatus.

FIG. 3 is a schematic view illustrating the top face of an embodiment ofthe image pickup apparatus.

FIGS. 4A and 4B are schematic views of a cross section of an embodimentof the image pickup apparatus.

FIG. 5 is a diagram illustrating driving pulses of an embodiment of theimage pickup apparatus.

FIGS. 6A to 6D are diagrams representing potential with an embodiment ofthe image pickup apparatus.

FIGS. 7A to 7D are diagrams representing potential with an embodiment ofthe image pickup apparatus.

FIGS. 8A to 8C are diagrams representing potential with an embodiment ofthe image pickup apparatus.

FIG. 9 is a diagram illustrating an equivalent circuit of an embodimentof the image pickup apparatus.

FIG. 10 is a schematic view illustrating the top face of an embodimentof the image pickup apparatus.

FIGS. 11A and 11B are schematic views of a cross section of anembodiment of the image pickup apparatus.

FIG. 12 is a diagram illustrating driving pulses of an embodiment of theimage pickup apparatus.

FIGS. 13A to 13D are diagrams representing potential with an embodimentof the image pickup apparatus.

FIGS. 14A to 14D are diagrams representing potential with an embodimentof the image pickup apparatus.

FIGS. 15A to 15C are diagrams representing potential with an embodimentof the image pickup apparatus.

FIG. 16 is a diagram representing potential with an embodiment of theimage pickup apparatus.

FIG. 17 is a diagram illustrating an equivalent circuit of an embodimentof the image pickup apparatus.

FIG. 18 is a schematic view illustrating the top face of an embodimentof the image pickup apparatus.

FIG. 19 is a block diagram of an image pickup system.

DESCRIPTION OF THE EMBODIMENTS

One disclosed feature of the embodiments may be described as a processwhich is usually depicted as a timing diagram. A timing diagram mayillustrate the timing relationships of several entities, such assignals, events, etc. Although a timing diagram may describe theoperations as a sequential process, some operations may be performed inparallel or concurrently. In addition, unless specifically stated, theorder of the operations or timing instants may be re-arranged.Furthermore, the timing or temporal distances may not be scaled ordepict the timing relationships in exact proportions.

According to one or more embodiments, image quality may be improved withan image pickup apparatus having a pixel configuration which enables aglobal electronic shutter.

The image pickup apparatus includes, within pixels, a photoelectricconversion unit, a first holding unit capable of holding a signal chargegenerated at the photoelectric conversion unit, and a second holdingunit capable of holding a signal charge transferred from the firstholding unit. According to such a configuration, a charge can be held atthe second holding unit during a period in which a signal chargegenerated at the photoelectric conversion unit is being held at thephotoelectric conversion unit and the first holding unit.

According to one or more embodiments, noise due to residual charge atthe first holding unit can be reduced by resetting the charge at thefirst holding unit with such a configuration.

One or more embodiments will be described with reference to thedrawings. An image pickup apparatus according to one or more embodimentsincludes multiple pixels. FIG. 2 illustrates an example of an equivalentcircuit of the pixels of the image pickup apparatus. As illustrated inFIG. 2, the pixels include a photoelectric conversion unit 8, a firstholding unit 10 which holds charge at a place or location different fromthe place or location of the photoelectric conversion unit 8, and asecond holding unit 12 which holds the charge held at the first holdingunit 10 at a place or location different from the place or location ofthe photoelectric conversion unit 8 and the first holding unit 10.

FIG. 3 illustrates an example of a top face view of the pixels. Thephotoelectric conversion unit 8 is disposed at a place indicated by anarea 101. The first holding unit 10 is disposed at a place or locationindicated by an area 103. The second holding unit 12 is disposed at aplace or location indicated by an area 105. Thus, the photoelectricconversion unit 8, the first holding unit 10, and the second holdingunit 12 are disposed at places or locations different from each other.

In one or more embodiments, the charge of the first holding unit 10 isdischarged. Accordingly, holding a charge at the first holding unit 10can be started in a state where there is little or not residual chargein the first holding unit 10, for example. As a result, image quality ofthe image pickup apparatus can be improved.

Discharge of the charge from the first holding unit 10 can be performedvia a path different from the transfer path via which the charge istransferred from the first holding unit 10 to the second holding unit12. In the example in FIG. 3, the transfer path via which the charge istransferred from the first holding unit 10 to the second holding unit 12is indicated as region 104, and the path via which the charge isdischarged from the first holding unit 10 is indicated as region 111.

From a different perspective, discharge of the charge from the firstholding unit 10 is performed when the second holding unit 12 is holdinga charge. From yet another perspective, transfer of charge from thefirst holding unit 10 to the second holding unit 12 is repeatedlyperformed, and part of the charge accumulated in the first holding unit10 is discharged in between transfers. Part of the charge accumulated inthe first holding unit 10 in between transfers is, for example, chargewhich has been mixed in the first holding unit 10 during a shutterperiod.

Also, one or more embodiments according to the image pickup apparatusmay include a first charge discharge unit 7. The first charge dischargeunit 7 includes a charge draining node serving as a charge dischargedestination. The charge draining node may be configured including asemiconductor region. Alternatively, the charge draining node may beconfigured including a conductor. Alternatively, the charge drainingnode may be configured including a semiconductor region and a conductorin contact with the semiconductor region. A predetermined voltage issupplied to the charge draining node. The predetermined voltage is, forexample, a power source voltage. According to such a configuration, theabove-described reset operation can be performed.

Note that discharge of charge is transfer of the charge from the firstholding unit 10 to a discharge destination. This movement of charge maybe realized by lowering the potential of the charge draining node lowerthan the potential of the first holding unit 10. Also, discharge of thecharge may be controlled by a control electrode.

Hereinafter, embodiments will be described. Here, “firstconductive-type” and “second conductive-type” are terms to be used forrepresenting mutually different conductive types. In the event that“first conductive-type” is N type, “second conductive-type” is P type.In the event that “first conductive-type” is P type, “secondconductive-type” is N type. Hereinafter, for simplification ofdescription, an example will be described wherein “firstconductive-type” is N type, and “second conductive-type” is P type.However, the disclosure is not restricted to this, and may also beapplied to a case where “first conductive-type” is P type, “secondconductive-type” is N type. In the event that the semiconductor regionmaking up the holding unit is N type, electrons caused due tophotoelectric conversion and of positive holes electrons are accumulatedin the holding unit. In the event that the semiconductor region makingup the holding unit is P type, electrons caused due to photoelectricconversion and of positive holes positive holes are accumulated in theholding unit.

Also, hereinafter, an embodiment of a pixel-amplification-type imagepickup apparatus having an amplifier unit for each pixel will bedescribed. The disclosure is not restricted to this, and may include acharge holding unit and various sensors having a transfer unit whichtransfers charge held at the holding unit.

First Embodiment

An embodiment of the image pickup apparatus will be described. Withregard to some embodiments, a feature thereof is in that pixels includea first holding unit 10, a second holding unit 12, and a first chargedischarging unit configured to discharge charge held at the firstholding unit 10.

FIG. 1 is an overall block diagram of image pickup apparatuses accordingto some embodiments. An image pickup apparatus 1 may be configured ofone chip using a semiconductor substrate. The image pickup apparatus 1includes multiple pixels disposed in an image pickup area 2. Further,the image pickup apparatus 1 includes a control unit 3. The control unit3 supplies a control signal, power supply voltage, and so forth to avertical scanning unit 4, a signal processing unit 5, and an output unit6.

The vertical scanning unit 4 supplies a driving pulse to multiple pixelsdisposed in the image pickup area 2. Usually, the vertical scanning unit4 supplies a driving pulse for each pixel row or for every multiplepixel rows. The vertical scanning unit 4 may be configured of a shiftregister or address decoder.

The signal processing unit 5 is configured to include a column circuit,a horizontal scanning circuit, and a horizontal output line. The columncircuit is configured of multiple circuit blocks which each receive thesignals of multiple pixels included in a pixel row selected by thevertical scanning unit 4. Each of the circuit blocks may be configuredof one or all of a memory unit, an amplifier circuit, a denoisingcircuit, and an analog-to-digital conversion circuit, or a combinationof these. These circuits may be a circuit which processes digitalsignals or may be a circuit which processes analog signals. Thehorizontal scanning circuit may be configured of a shift register oraddress decoder.

The output unit 6 outputs a signal transmitted via a horizontal outputline out of the image pickup apparatus 1. The output unit 6 isconfigured to include a buffer or amplifier circuit.

FIG. 2 illustrates an equivalent circuit of image pickup apparatusesaccording to some embodiments. Here, though six pixels in a total of tworows by three columns are illustrated, an image pickup area may beconfigured by an even greater number of pixels being disposed.

The photoelectric conversion unit 8 converts incident light into signalcharge (electron or positive hole). A photodiode is illustrated as anexample of the photoelectric conversion unit 8.

The first charge transfer unit 9 transfers charge generated at thephotoelectric conversion unit 8 to a circuit element on the subsequentstage. Hereinafter, a case where electrons are employed as signal chargewill be described as an example. The first charge transfer unit 9 isconfigured to include a control electrode disposed on the semiconductorsubstrate via an insulating film.

The first holding unit 10 holds electrons generated at the photoelectricconversion unit 8. The second charge transfer unit 11 transfers theelectrons held at the first holding unit 10 to a circuit element on thesubsequent stage. The second charge transfer unit 11 is configured toinclude a control electrode disposed on the semiconductor substrate viaan insulating film.

The second holding unit 12 holds the electrons transferred from thefirst holding unit 10 via the second charge transfer unit 11. The thirdcharge transfer unit 13 transfers the electrons held at the secondholding unit 12 to the circuit element on the subsequent stage. Thethird charge transfer unit 13 may be configured to include a controlelectrode disposed on the semiconductor substrate via the insulatingfilm.

An input node 14 of an amplifier unit 15 is configured so as to holdelectrons transferred from the second holding unit 12 via the thirdcharge transfer unit 13. The input node 14 of the amplifier unit 15 maybe configured to include a floating diffusion area (hereinafter, FDarea) disposed in the semiconductor substrate. The amplifier unit 15outputs a signal based on electrons transferred to the input node 14 toa vertical signal line 20. Here, a MOS transistor (hereinafter,amplifier transistor) is employed as the amplifier unit 15. For example,the amplifier transistor makes up a source follower circuit. Also, thethird charge transfer unit 13 is disposed in an electrical path betweenthe input node 14 of the amplifier unit 15 and the second holding unit12. That is to say, the input node 14 of the amplifier unit 15 and thesecond holding unit 12 are different nodes. The configuration is notrestricted to such an example, and as long as two nodes are configuredso as to be electrically insulated, these nodes are different nodes.

A first charge discharging unit 7 transfers the electrons held at thefirst holding unit 10 to an overflow drain area (hereinafter, OFD area).The OFD area is a charge discharging node from which charge isdischarged. The OFD area may be configured of an N-type semiconductorregion electrically connected to the wiring 16 which supplies powersupply voltage, for example. The first charge discharging unit 7 isconfigured to include a control electrode disposed on the semiconductorsubstrate via the insulating film. Discharging of the charge of thefirst holding unit 10 is controlled by voltage to be supplied to thecontrol electrode of the first charge discharging unit 7.

With some embodiments, an electronic shutter operation may be performedby the first charge transfer unit 9 and first charge discharging unit 7.That is to say, a period to discharge electrons generated at thephotoelectric conversion unit 8 (shutter period) and a period toaccumulate electrons (exposure period) may be controlled by controllingthe first charge transfer unit 9 and first charge discharging unit 7.

A reset unit 17 supplies reference voltage to the input node 14 of theamplifier unit 15. In other words, the reset unit 17 resets the voltageat the input node 14 of the amplifier unit 15. Here, a MOS transistor(hereinafter, reset transistor) is employed as the reset unit 17. Notethat, with some embodiments, the reset unit 17 may be omitted. This isbecause reset of a pixel may be performed by the first chargedischarging unit 7.

A selecting unit 18 selects each pixel to read out the signal of a pixelto a vertical signal line 20 for each pixel or for every pixel row.Here, a MOS transistor (hereinafter, selecting transistor) is employedas the selecting unit 18. Note that the selecting unit 18 may bedisposed in a path between the amplifier unit 15 and the vertical signalline 20. Alternatively, the selecting unit 18 may be omitted. With anexample of the selecting unit 18 being omitted, a pixel is selected byvoltage that the reset unit 17 supplies to the input node 14 of theamplifier unit 15.

Predetermined voltage is supplied to the drain of the reset transistorand the drain of the selecting transistor via a wiring 19. Thepredetermined voltage is power supply voltage, for example. Note that,in the event that the selecting unit 18 has been disposed in a pathbetween the amplifier unit 15 and the vertical signal line 20, and alsoin the event that the selecting unit 18 has been omitted, the drain ofthe amplifier transistor is connected to the wiring 19.

A reset control wiring 21 supplies a driving pulse PRES to the gate ofthe reset transistor. A selection control wiring 22 supplies a drivingpulse PSEL to the gate of the selecting transistor. A third transfercontrol wiring 23 supplies a driving pulse PTX3 to a control electrode(hereinafter, third control gate) making up the third charge transferunit 13. A second transfer control wiring 24 supplies a driving pulsePTX2 to a control electrode (hereinafter, second control gate) making upthe second charge transfer unit 11. A first transfer control wiring 25supplies a driving pulse PTX1 to a control electrode (hereinafter, firstcontrol gate) making up the first charge transfer unit 9. A fourthtransfer control wiring 26 supplies a driving pulse PMRES1 to a controlelectrode (hereinafter, fourth control gate) making up the first chargedischarging unit 7. The height of the potential barrier of thesemiconductor region below each of the control gates may be changed bychanging a pulse value to be supplied to each of the control gates. Thatis to say, each of the charge transfer units and charge discharging unitmay control the potential of the charge transfer path to be disposedbelow the control electrode.

With some embodiments, at the pixel configuration illustrated with theequivalent circuit exemplified in FIG. 2, the electrical path betweenthe photoelectric conversion unit 8 and the first holding unit 10 mayhave the following configuration. The configuration thereof is aconfiguration wherein the first charge transfer unit 9 disposed in theelectrical path between the photoelectric conversion unit 8 and thefirst holding unit 10 is in a non-conductive state, and electrons areallowed to be moved from the photoelectric conversion unit 8 to thefirst holding unit 10. Here, the non-conductive state is a state inwhich of pulse values to be supplied to the first charge transfer unit9, a pulse value to generate the highest potential barrier has beensupplied. Accordingly, the first charge transfer unit 9 does not have tobe so-called completely off, and the non-conductive state of the firstcharge transfer unit 9 also includes a state in which some sort ofpotential barrier has occurred as compared to a case where the firstcharge transfer unit 9 has completely been turned on.

For example, in the event that a MOS transistor is the first chargetransfer unit 9, a specific configuration may be made by this MOStransistor having an embedded channel configuration. More generallyspeaking, this configuration is a configuration wherein there is aportion in an area deeper than the surface where the potential barrierfor an electrode is lower than the surface when the first chargetransfer unit 9 is in a non-conductive state. In this case, a drivingpulse to be supplied to the first charge transfer unit 9 may be a fixedvalue. That is to say, fixed potential barrier may be employed insteadof a configuration wherein two states of a conductive state and anon-conductive state are switchable.

According to such a configuration, when light is input to thephotoelectric conversion unit 8, almost of electrons generated byphotoelectric conversion are moved to the first holding unit 10 duringthe exposure period. Accordingly, the accumulation periods of all of thepixels disposed in the image pickup area 2 may be aligned by performingtransfer of charge from the first holding unit 10 to the second holdingunit 12 in parallel.

Further, when the first charge transfer unit 9 is in a non-conductivestate, a hole is accumulated on the surface. Also, the channel whereelectrons move exists in a predetermined depth portion from the surface,and accordingly, influence of dark current may be reduced as compared toa case where electrons move in an interface between the semiconductorsubstrate and the insulating film.

Alternatively, the electrical path between the photoelectric conversionunit 8 and the first holding unit 10 may have another configuration. Theother configuration is a configuration wherein the first charge transferunit 9 disposed in the electrical path between the photoelectricconversion unit 8 and the first holding unit 10 is in a non-conductivestate, and no electrons are moved from the photoelectric conversion unit8 to the first holding unit 10. Here, the non-conductive state is astate in which of pulse values to be supplied to the first chargetransfer unit 9, a pulse value to generate the highest potential barrierhas been supplied. In other words, this is a configuration wherein themajority of electrons generated by photoelectric conversion isaccumulated in the photoelectric conversion unit 8.

During a period for accumulating electrons at the photoelectricconversion unit 8, a lower potential barrier than the potential barrierat the first charge transfer unit 9 is formed around the photoelectricconversion unit 8, and accordingly, a configuration wherein no electronsare moved from the photoelectric conversion unit 8 to the first holdingunit 10 may be obtained. As for a specific configuration, when the firstcharge transfer unit 9 is in a non-conductive state, a potential barrierto be formed below the first control electrode is higher than apotential barrier to be formed between the photoelectric conversion unit8 and another circuit element. The other circuit element is the OFD areaof the first charge discharging unit 7, for example. Or, the othercircuit element is the reset transistor, selecting transistor, amplifiertransistor, or the like.

According to such a configuration, the majority of electrons generatedby photoelectric conversion at the time of light being input to thephotoelectric conversion unit 8 is accumulated in the photoelectricconversion unit 8 during the exposure period. Accordingly, with all ofthe pixels disposed in the image pickup area 2, charge accumulated inthe photoelectric conversion units 8 is simultaneously transferred tothe first holding unit 10, whereby the accumulation periods of all ofthe pixels may be aligned.

Specific configurations of pixels of some embodiments will be describedwith reference to FIGS. 3, 4A, and 4B. Members having the same name as amember described in FIG. 2 have the same function, and accordingly,detailed description will be omitted.

FIG. 3 illustrates a top view of image pickup apparatuses according tosome embodiments. Here, though six pixels in a total of two rows bythree columns are illustrated, an image pickup area may be configured byan even greater number of pixels being disposed.

Pixels 100 are configured of an N-type semiconductor region 101 makingup the photoelectric conversion unit 8, a control electrode 102 makingup the first charge transfer unit 9, an N-type semiconductor region 103making up the first holding unit 10, a control electrode 104 making upthe second charge transfer unit 11, an N-type semiconductor region 105making up the second holding unit 12, a control electrode 106 making upthe third charge transfer unit 13, an FD area 107, a reset transistor108, an amplifier transistor 109, and a selecting transistor 110.Further, the pixels 100 include a control electrode 111 and an OFD area112 which make up the first charge discharging unit 7. The FD area 107is configured to include an N-type semiconductor region where electronsheld at the second holding unit 12 are transferred. The OFD area 112 isconfigured to include an N-type semiconductor region where charge fromthe first holding unit 10 is discharged.

Note that the OFD area 112 may be shared with the source or drain of thereset transistor, selecting transistor, or amplifier transistor. That isto say, the charge of the first holding unit 10 is transferred to thesource or drain of one of the reset transistor, selecting transistor,and amplifier transistor. According to such a configuration, the area ofthe photoelectric conversion unit 8 may be increased, and accordingly,sensitivity may be improved.

A P-type semiconductor region 114 is disposed below the N-typesemiconductor region 103. The N-type semiconductor region 103 and P-typesemiconductor region 114 make up a PN junction. A P-type semiconductorregion 115 is disposed below the N-type semiconductor region 105. TheN-type semiconductor region 105 and P-type semiconductor region 115 makeup a PN junction. Note that, with some embodiments, the P-typesemiconductor region 114 and 115 may be omitted.

A feature of some embodiments is in that the first charge dischargingunit 7 which discharges the charge of the N-type semiconductor region103 of the first holding unit 10 in the pixels 100. The first chargedischarging unit 7 may be a MOS transistor made up of the controlelectrode 111, N-type semiconductor region 103, and OFD area 112. Thecontrol electrode 111 included in the first charge discharging unit 7 isdisposed adjacent to the N-type semiconductor region 103 with a planarview. According to such displacement, the first charge discharging unit7 may discharge the charge of the first holding unit 10.

The charge of the photoelectric conversion unit 8 is passed through thesemiconductor region below the control electrode 102 and transferred tothe first holding unit 10. That is to say, the path where charge istransferred from the photoelectric conversion unit 8 to the firstholding unit 10 is disposed below the control electrode 102. The chargeof the first holding unit 10 is passed through the semiconductor regionbelow the control electrode 102 and transferred to the second holdingunit 12. That is to say, the path where charge is transferred from thefirst holding unit 10 to the second holding unit 12 is disposed belowthe control electrode 104. Also, the charge of the first holding unit 10is passed through the semiconductor region below the control electrode111 and discharged to the OFD area 112. That is to say, the path wherecharge is discharged from the first holding unit 10 is disposed belowthe control electrode 111. In this manner, the charge of the firstholding unit 10 is discharged via a path different from both of thetransfer path of charge from the photoelectric conversion unit 8 to thefirst holding unit 10 and the transfer path of charge from the firstholding unit 10 to the second holding unit 12.

FIGS. 4A and 4B illustrate schematic views of the cross section alongthe lines IVA-IVA and IVB-IVB in FIG. 3. Members having the samefunction in FIG. 2 will be denoted with the same reference numeral, anddetailed description will be omitted.

The image pickup apparatuses according to some embodiments include asemiconductor substrate 300 a and an insulating film 300 b disposedthereon. The semiconductor substrate 300 a is silicon, for example. Thesemiconductor substrate 300 a may include a semiconductor region formedwith epitaxial growth. The insulating film 300 b is a silicon oxidefilm, for example. A semiconductor region is formed within thesemiconductor substrate 300 a. Also, a control electrode is disposed onthe semiconductor substrate 300 a via the insulating film 300 b.

An N-type semiconductor region 301 is disposed in the semiconductorsubstrate 300 a. A P-type semiconductor region 302 is disposed on theN-type semiconductor are 301. The N-type semiconductor region 101 isdisposed so as to make up a PN junction with the P-type semiconductorregion 302. A P-type semiconductor region 303 is disposed on the surfaceside of the N-type semiconductor region 101, i.e., a side close to theinsulating film 300 b. A so-called embedded-type photodiode is made upof the P-type semiconductor region 302, N-type semiconductor region 101,and P-type semiconductor region 303.

Electrons generated at the photoelectric conversion unit 8 move in afirst channel 304, and reach the N-type semiconductor region 103 whichmakes up the first holding unit 10. The electrons held at the N-typesemiconductor region 103 move in a second channel 305, and reach anN-type semiconductor region 105 which makes up the second holding unit12. The electrons held at the N-type semiconductor region 105 move in athird channel 306, and reach the N-type semiconductor region 107 whichmakes up the FD area. Also, the electrons of the first holding unit 10may be discharged to the OFD area 112 via a channel 307 disposed belowthe control electrode 111.

The control electrode 102 is disposed on the upper portion of the firstchannel 304 via the insulating film 300 b. With some embodiments, thecontrol electrode 102 includes a portion 102 a disposed on the N-typesemiconductor region 103. The control electrode 102 is shared by thefirst charge transfer unit 9 and first holding unit 10. That is to say,potential between the photoelectric conversion unit 8 and the firstholding unit 10 is controlled by voltage to be applied to the controlelectrode 102. Additionally, the potential of the first holding unit 10is controlled by voltage to be applied to the control electrode 102. Thefirst charge transfer unit 9 is configured to include the first channel304 and a portion of the control electrode 102 disposed on the firstchannel 304 via the insulating film.

The first holding unit 10 includes the N-type semiconductor region 103and the P-type semiconductor region 114 which makes up a PN junctionwith the N-type semiconductor region 103. Electrons are accumulated bythe N-type semiconductor region 103 making up PN junction capacitance.Further, the first holding unit 10 is configured to include the portion102 a of the control electrode 102 disposed on the N-type semiconductorregion 103 via the insulating film. An inversion layer may be formed onthe interface 300 side of the N-type semiconductor region 103 by voltageto be applied to the control electrode 102. Thus, mixing of dark currentinto the first holding unit 10 may be reduced.

The control electrode 104 is disposed on the second channel 305 via theinsulating film 300 b. With some embodiments, the control electrode 104includes a portion 104 a disposed on the N-type semiconductor region105. The control electrode 104 is shared by the second charge transferunit 11 and second holding unit 12. That is to say, potential betweenthe first holding unit 10 and the second holding unit 12 is controlledby voltage to be applied to the control electrode 104. Additionally, thepotential of the second holding unit 12 is controlled by voltage to beapplied to the control electrode 104. The second charge transfer unit 11is configured to include the second channel 305 and a portion of thecontrol electrode 104 disposed on the second channel 305 via theinsulating film.

The second holding unit 12 includes the N-type semiconductor region 105and the P-type semiconductor region 115 which makes up a PN junctionwith the N-type semiconductor region 105. Electrons are accumulated bythe N-type semiconductor region 105 making up PN junction capacitance.Further, the second holding unit 12 is configured to include the portion104 a of the control electrode 104 disposed on the N-type semiconductorregion 105 via the insulating film. An inversion layer may be formed onthe interface 300 side of the N-type semiconductor region 105 by voltageto be applied to the control electrode 104. Thus, mixing of dark currentinto the second holding unit 12 may be reduced.

The control electrode 106 is disposed on the third channel 306 via theinsulating film 300 b. The third charge transfer unit 13 is configuredto include the third channel 306 and the control electrode 106 disposedon the third channel 306 via the insulating film.

A plug which is not illustrated is connected to the FD area 107 and OFDarea 112. The FD area 107 is connected to the gate electrode of theamplifier transistor via the plug. The OFD area 112 is connected to awiring 16 which is not illustrated, via the plug. The plug is configuredof metal such as tungsten or the like.

Also, the P-type semiconductor region 114 is disposed below the N-typesemiconductor region 103. The P-type semiconductor region 114 may bedisposed below a portion of the N-type semiconductor region 103, or maybe disposed below the whole of the N-type semiconductor region 103. TheN-type semiconductor region 103 and P-type semiconductor region 114 makeup a PN junction. The impurity concentration of the P-type semiconductorregion 114 is higher than the impurity concentration of the P-typesemiconductor region disposed below the P-type semiconductor region 114.For example, with some embodiments, the impurity concentration of theP-type semiconductor region 114 is higher than the impurityconcentration of the P-type semiconductor region 302. According to sucha configuration, extension of the depletion layer from the N-typesemiconductor region 103 may be reduced, and accordingly, charge may betransferred from the first holding unit 10 with low voltage.

Also, the P-type semiconductor region 115 is disposed below the N-typesemiconductor region 105. The P-type semiconductor region 115 may bedisposed just below a portion of the N-type semiconductor region 105, ormay be disposed below the whole of the N-type semiconductor region 105.The N-type semiconductor region 105 and P-type semiconductor region 115make up a PN junction. The impurity concentration of the P-typesemiconductor region 115 is higher than the impurity concentration ofthe P-type semiconductor region disposed below the P-type semiconductorregion 115. For example, with some embodiments, the impurityconcentration of the P-type semiconductor region 115 is higher than theimpurity concentration of the P-type semiconductor region 302. Accordingto such a configuration, extension of the depletion layer from theN-type semiconductor region 105 may be reduced, and accordingly, chargemay be transferred from the second holding unit 12 with low voltage.

Note that either or both of the P-type semiconductor regions 114 and 115may be omitted. With an example of the P-type semiconductor region 114being omitted, the P-type semiconductor region 302 disposed below theN-type semiconductor region 103 may have an impurity distribution wherethe impurity concentration becomes higher the deeper the depth is, or aneven impurity distribution.

Next, the impurity concentration of each of the semiconductor regionswill be described. Note that the impurity concentration of each of thesemiconductor regions is not restricted to this, and may be changed asappropriate.

It is desirable that the impurity concentration of the N-typesemiconductor region 103 and the impurity concentration of the N-typesemiconductor region 105 are each higher than the impurity concentrationof the N-type semiconductor region 101. Thus, the charge holdingcapacitance of the first holding unit 10 and the charge holdingcapacitance of the second holding unit 12 may be increased.Alternatively, the sensitivity of the photoelectric conversion 8 may beimproved.

It is desirable that the impurity concentration of the P-typesemiconductor region 303 is higher than that of the P-type semiconductorregion 302. Alternatively, it is desirable that the impurityconcentration of the P-type semiconductor region 303 is higher than thatof the N-type semiconductor region 101. According to such aconfiguration, noise due to dark current at the photoelectric conversionunit 8 may be reduced.

A light shielding member 113 is disposed above the first holding unit 10and second holding unit 12. The first holding unit 10 and second holdingunit 12 are shielded by the light shielding member 113. Preferably, thelight shielding member 113 shields the entire light to be input to thefirst holding unit 10 and second holding unit 12. The end portion on thephotoelectric conversion unit 8 side of the light shielding member 113is closer to the photoelectric conversion unit 8 than the end portion onthe photoelectric conversion unit 8 side of the first holding unit 10.The end portion on the FD area 107 side of the light shielding member113 is closer to the FD area 107 than the end portion on the FD area 107side of the second holding unit 12.

However, the configuration is not restricted to this, and an arrangementmay be made wherein in the event that the control electrode 102 isshared by the first charge transfer unit 9 and first holding unit 10, atleast the end portion of the photoelectric conversion unit 8 side of thecontrol electrode 102 is not covered. According to such a configuration,influence of the light shielding member 113 as to the photoelectricconversion unit 8 is reduced, and accordingly, the sensitivity of thephotoelectric conversion unit 8 may be improved. Further, influence asto a pixel position of light to be input with a certain angle againstthe vertical direction may be reduced. Alternatively, electronssubjected to photoelectric conversion at the N-type semiconductor region103 or P-type semiconductor region 302 which makes up the first holdingunit 10 may be accumulated at the N-type semiconductor region 103. Thus,the sensitivity of pixels may be improved.

Note that the overall of the first holding unit 10 does not have to becovered with the light shielding member 113. For example, in order todispose a conductor for supplying a driving pulse to the controlelectrode 102 which makes up the first holding unit 10, an opening maybe provided to the light shielding member 113.

The overall of the second holding unit 12 does not have to be coveredwith the light shielding member 113. For example, in order to dispose aconductor for supplying a driving pulse to the control electrode 104which makes up the second holding unit 12, an opening may be provided tothe light shielding member 113.

Metal making up a wiring layer may be employed as the light shieldingmember 113. Alternatively, there may be employed metal making up a plugfor electrically connecting different wiring layers or between a wiringand a semiconductor region. It is desirable to dispose the lightshielding member 113 in a place closer to the semiconductor substrate300 a as much as possible. It is desirable to employ metal making up awiring layer disposed closest to the semiconductor substrate 300 a ofthe multiple wiring layers, or a metal plug which electrically connectsthe wiring layer of the lowest layer and a semiconductor region.Alternatively, a metal specifically for the light shielding member 113may be disposed between the wiring layer of the lowest layer and thesemiconductor substrate.

FIGS. 4A and 4B illustrate the light shielding member 113 alone disposedon the first holding unit 10. However, a light shielding member may bedisposed on a transistor making up another pixel circuit. Alternatively,a transistor making up another pixel circuit may be shielded by wiring.Transistors making up another pixel circuit include the above-mentionedrest transistor, selecting transistor, amplifier transistor, and soforth.

Next, a driving method according to some embodiments will be described.FIG. 5 illustrates a driving pulse diagram of the image pickup apparatusaccording to some embodiments. This is a pulse diagram illustrating acase of performing global electronic shutter operation wherein exposureperiods agree regarding all of the pixels disposed in the image pickuparea 2. The numbers in parentheses indicate the number of rows, and inthe present drawing, driving pulses to be supplied to the pixels in thefirst and second rows are illustrated. PSEL indicates a driving pulse tobe supplied to the gate of the selecting transistor. PRES indicates adriving pulse to be supplied to the gate of the reset transistor. PTX1indicates a driving pulse to be supplied to the first control gate. PTX2indicates a driving pulse to be supplied to the second control gate.PTX3 indicates a driving pulse to be supplied to the third control gate.PMRES1 indicates a driving pulse to be supplied to the fourth controlgate. PTS indicates a driving pulse for performing sample hold of alight signal using, for example, the memory unit disposed in the columncircuit. PTN indicates a driving pulse for performing sample hold of anoise signal using, for example, the memory unit disposed in the columncircuits. All of the driving pulses are in a high level at the time of aconductive state.

At point-in-time t1 and theretofore, the PRES in all of the rows in theimage pickup area 2 are in a high level. Therefore, voltage at the inputnode of the amplifier unit 15 is reset. Here, the other pulsesillustrated in FIG. 5 are all in a low level. Thus, electrons generatedby photoelectric conversion are accumulated at the photoelectricconversion unit 8 and first holding unit 10. That is to say, theexposure period has started prior to the point-in-time t1. Of electronsgenerated at the photoelectric conversion unit 8, predetermined amountof electrons move to the first holding unit 10.

At the point-in-time t1, in a state in which the PRES maintains a highlevel, with all of the pixels disposed in the image pickup area 2, thePTX3 makes the transition from a low level to a high level. Thus, thesecond holding unit 12 is reset. That is to say, the charge of thesecond holding unit 12 is discharged via the reset unit 17. Atpoint-in-time t2, with all of the pixels disposed in the image pickuparea 2, the PTX3 makes the transition from a high level to a low level.Thus, reset of the second holding unit 12 is completed.

After elapsing of a predetermined period following the point-in-time t2,at point-in-time t3 the PTX1 in all of the rows in the image pickup area2 makes the transition from a low level to a high level, atpoint-in-time t4 the PTX1 in all of the rows in the image pickup area 2makes the transition from a high level to a low level. According to thisoperation, the electrons remaining in the photoelectric conversion unit8 are transferred to the first holding unit 10. According to thisoperation, the exposure periods are ended.

At point-in-time t5, the PTX2 in all of the rows disposed in the imagepickup area 2 make the transition from a low level to a high level, andat point-in-time t6 the PTX2 in all of the rows disposed in the imagepickup area 2 make the transition from a high level to a low level.According to this operation, the electrons held at the first holdingunits 10 are transferred to the second holding unit 12.

At point-in-time t7, the PTX1 and PMRES1 in all of the rows disposed inthe image pickup area 2 makes the transition from a low level to a highlevel. Thus, electrons generated at the photoelectric conversion unit 8are moved to the first holding unit 10, and the electrons of the firstholding unit 10 are discharged to the OFD area 112. That is to say, theelectrons generated by photoelectric conversion are not accumulated butdischarged. In this manner, with some embodiments, when the first chargetransfer unit 9 and first charge discharging unit 7 are in a conductivestate, this is a shutter period.

At point-in-time t8, the PSEL(1) makes the transition from a low levelto a high level. According to this operation, the signals of the pixelsat the first row are placed a state enabled to be output to the verticalsignal line 20. Further, at the point-in-time t8, the PRES(1) makes thetransition from a high level to a low level. Thus, the reset operationsof the input nodes 14 of the amplifier elements 15 are completed.

At point-in-time t9, the PTN makes the transition from a low level to ahigh level, and point-in-time t10 the PTN makes the transition from ahigh level to a low level. According to this operation, a noise signalis held at, for example, the memory unit for noise signals disposed inthe column circuit.

At point-in-time t11, the PTX3(1) makes the transition from a low levelto a high level, and at point-in-time t12 the PTX3(1) makes thetransition from a high level to a low level. According to thisoperation, electrons held at the second holding units 12 of the pixelsat the first row are transferred to the input nodes 14 of the amplifierelements 15.

At point-in-time t13, the PTS makes the transition from a low level to ahigh level, and at point-in-time t14 the PTS makes the transition from ahigh level to a low level. According to this operation, a light signalon which a noise signal is superimposed is held at, for example, thememory unit for light signals disposed in the column circuit.

At point-in-time t15, the PSEL(1) makes the transition from a high levelto a low level. According to this operation, the readout periods of thesignals of the pixels at the first row are ended. The readout periods ofthe pixels at the first row are a period from the point-in-time t8 tothe point-in-time t15. Further, at the point-in-time t15, the PRES(1)makes the transition from a low level to a high level. Thus, reset forthe input nodes 14 of the amplifier elements 15 of the pixels of thefirst row is started.

After this, with a period from point-in-time t16 to point-in-time t23,readout of the signals of the pixels at the second row are performed.This operation is the same operation as the first row, and accordingly,detailed description will be omitted. The operation at eachpoint-in-time from the point-in-time t16 to the point-in-time t23 is thesame as the operation at each point-in-time from the point-in-time t8 tothe point-in-time t15 except that objects for driving pulses to be setto a high level belong to the second row.

Here, at point-in-time tAcc between the point-in-time t15 and thepoint-in-time t16, the PTX1 and PMRES1 in all of the rows disposed inthe image pickup apparatus make the transition from a high level to alow level. Thus, electrons generated by photoelectric conversion areaccumulated at the photoelectric conversion unit 8 and first holdingunit 10. That is to say, the exposure period starts.

With some embodiments, until the exposure period starts at thepoint-in-time tAcc, the PMRES1 is in a high level. That is to say,before the exposure period starts, the charge of the first holding unit10 may be discharged to the OFD area 112. Preferably, all of theelectrons of the first holding units 10 are discharged before theexposure period starts. Accordingly, when starting accumulation ofelectrons at the first holding units 10, the electrons remaining at thefirst holding units 10 may be reduced or may completely be discarded.

In other words, after charge is transferred from the first holding unit10 to the second holding unit 12 at the point-in-time t6, the chargeheld at the first holding units 10 is discharged during a period fromthe point-in-time t7 to the point-in-time tAcc. At the point-in-timetAcc and thereafter, until charge is transferred from the first holdingunit 10 to the second holding unit 12 next, the charge held at the firstholding unit 10 is not discharged. That is to say, part of the chargeheld at the first holding units 10 is discharged between transfer ofcharge and transfer of charge.

Also, at the point-in-time tAcc, the second holding units 12 of thepixels at the second low hold electrons. With some embodiments, thefirst charge discharging unit 7 which discharges the electrons of thefirst holding unit 10 is disposed, whereby the electrons of the firstholding unit 10 may be discharged when the second holding unit 12 holdselectrons.

Note that FIG. 5 illustrates an example for staring an exposure periodat between the point-in-time t15 and point-in-time t16. However, thepoint-in-time tAcc to start an exposure period is not restricted tothis. The point-in-time tAcc to start an exposure period may be any timeas long as the point-in-time is after the point-in-time t6 when theelectrons of the first holding unit 10 are transferred.

According to such an operation, the exposure periods may be equalized atall of the pixels disposed in the image pickup area 2. With the presentoperation, up to transfer of the first holding unit 10 is performed atthe entire image pickup surface at the same time. Specific point-in-timethereof is the point-in-time t6. Thereafter, readout of all of the rowsat the image pickup area 2 is performed by repeating the readoutoperation.

Next, potentials at the pixels according to some embodiments will bedescribed. FIGS. 6 to 8 illustrate a relation of height of a potentialbarrier at each of the periods in the driving pulse diagram illustratedin FIG. 5. FIGS. 6 to 8 illustrate the potentials of the OFD area 112,first charge discharging unit 7, photoelectric conversion unit 8, firstcharge transfer unit 9, first holding unit 10, second charge transferunit 11, second holding unit 12, third charge transfer unit 13, andinput node 14 (FD area 107). The potentials of pixels according to someembodiments are illustrated with a solid line.

Note that, with the present Specification, the potential is thepotential energy of signal charge. For example, in the event that signalcharge is electrons, the higher the voltage applied to a controlelectrode is, the lower the potential of the semiconductor region belowthe control electrode becomes. This is because electrons have negativecharge. At an area where voltage is high, the potential energy ofelectrons is low. On the other hand, in the event that signal charge isa hole, the higher the voltage applied to a control electrode is, thehigher the potential of the semiconductor region below the controlelectrode becomes. This is because holes have positive charge. At anarea where voltage is high, the potential energy of a hole is high. InFIGS. 6A to 8C, the lower portions in the drawings represent lowpotential for signal charge, and the upper portions in the drawingsrepresent high potential for signal charge.

FIG. 6A is a diagram illustrating a potential state before thepoint-in-time t1. The first charge transfer unit 9, second chargetransfer unit 11, third charge transfer unit 13, and first chargedischarging unit 7 are in a non-conductive state. That is to say, apotential barrier to be generated at the first charge transfer unit 9and first charge discharging unit 7 is high. At this time, it isdesirable that the potential of the first charge discharging unit 7 ishigher than the potential of the first charge transfer unit 9. Also,when the first charge transfer unit 9 and first charge discharging unit7 are in a non-conductive state, it is desirable that the potential ofthe first holding unit 10 is lower than the potential of thephotoelectric conversion unit 8. Thus, the charge generated byphotoelectric conversion is held at the photoelectric conversion unit 8and first holding unit 10.

Note that, in the event that the potential of the first charge transferunit 9 is higher than the potential of the photoelectric conversion unit8, little amount of electrons are accumulated in the photoelectricconversion units 8 alone. In this case, in the event that a certainamount or more of electrons are generated at the photoelectricconversion units 8, the electrons of the first holding unit 10 crossesover a potential barrier generated at the first charge transfer unit 9and moves. Specifically, in the event that predetermined amount or morelight has been input, electrons are held at the photoelectric conversionunits 8 and first holding units 10 during an exposure period.

FIG. 6B is a diagram illustrating a potential state during a period fromthe point-in-time t1 to the point-in-time t2. As described in FIG. 5,with the period from the point-in-time t1 to the point-in-time t2, apulse in a high level is supplied to the third charge transfer unit 13.That is to say, a potential barrier generated at the third chargetransfer unit 13 is in a low state. Thus, the electrons of the secondholding unit 12 are discharged to the drain (not illustrated) of thereset transistor. Preferably, no electrons exist in the second holdingunit 12.

At this time, it is a desirable state that the potentials decrease inorder from the second holding unit 12 to the input node 14 of theamplifier unit 15. Specifically, the potential of the second holdingunit 12 may be higher than the potential of the third charge transferunit 13, and the potential of the third charge transfer unit 13 may behigher than the potential of the input node 14.

FIG. 6C is a diagram illustrating a potential state during a period fromthe point-in-time t2 to the point-in-time t3. The third charge transferunit 13 is in a non-conductive state, and accordingly, the potentialbarrier at the third charge transfer unit 13 becomes high. This state isthe same as with FIG. 6A.

FIG. 6D is a diagram illustrating a potential state during a period fromthe point-in-time t3 to the point-in-time t4. At this time, the firstcharge transfer unit 9 is in a conductive state. Thus, electronsaccumulated at the photoelectric conversion unit 8 is transferred to thefirst holding unit 10. In order to improve transfer efficiency ofelectrons from the photoelectric conversion unit 8, it is desirable thata potential barrier at the time of conduction of the first chargetransfer unit 9 is lower than the potential of the photoelectricconversion unit 8. Further, it is desirable that the potential of thefirst holding unit 10 is lower than the potential of the photoelectricconversion unit 8.

With some embodiments, the control electrode 102 is shared by the firstcharge transfer unit 9 and first holding unit 10, and accordingly, whena driving pulse to cause the first charge transfer unit 9 to be in aconductive state is supplied, the potential of the first holding unit 10also decreases. Thus, as illustrated in FIG. 6D, potential in the eventthat there are no electrons at the first holding unit 10 may be lowerthan the potential of the second holding unit 12.

FIG. 7A is a diagram illustrating a potential state during a period fromthe point-in-time t4 to the point-in-time t5. This illustrates a stateafter the first charge transfer unit 9 enters a non-conductive state,and also before the second charge transfer unit 11 enters a conductivestate. Also, the first charge discharging unit 7 is in a non-conductivestate. Therefore, the amount of electrons determined by potentialbarriers generated at the first charge transfer units 9 and first chargedischarging units 7 have been accumulated in the first holding units 10.

FIG. 7B is a diagram illustrating a potential state during a period fromthe point-in-time t5 to the point-in-time t6. The second charge transferunit 11 is in a conductive state. Thus, the electrons held at the firstholding unit 10 are transferred to the second holding unit 12 via thesecond charge transfer unit 11. In order to improve the transferefficiency of electrons from the first holding unit 10, it is desirablethat a potential barrier at the time of conduction of the second chargetransfer unit 11 is lower than the potential of the first holding unit10. Further, it is desirable that the potential of the second holdingunit is lower than the potential of the first holding unit 10.

With some embodiments, the control electrode 104 is shared by the secondcharge transfer unit 11 and second holding unit 12. Therefore, when adriving pulse to cause the second charge transfer unit 11 to be in aconductive state is supplied, the potential of the second chargetransfer unit 11 decreases, and accompanied with this, the potential ofthe second holding unit 12 also decreases. Note that, when all of thecharge transfer units and the first charge discharging unit 7 are in anon-conductive state, the potentials of the first holding unit 10 andsecond holding unit 12 may be the same. Alternatively, at this time, thepotential of the first holding unit 10 may be higher than the potentialof the second holding unit 12.

FIG. 7C is a diagram illustrating a potential state during a period fromthe point-in-time t6 to the point-in-time t7. The second charge transferunit 11 is in a non-conductive state. Also, the third charge transferunit 13 is in a non-conductive state. Thus, the second holding unit 12holds electrons.

FIG. 7D illustrates potential states of the pixels at the first rowduring a period from the point-in-time t7 to the point-in-time t11, andpotential states of the pixels at the second row during a period fromthe point-in-time t7 to the point-in-time tAcc. This is a period afterthe second charge transfer unit 11 enters a non-conductive state untilthe third charge transfer unit 13 enters a conductive-state. The lengthof this period may differ for each pixel row. Both of the second chargetransfer unit 11 and third charge transfer unit 13 are in anon-conductive state, and the second holding unit 12 accumulateselectrons according to these potential barriers.

Also, at the point-in-time t7, the first charge transfer unit 9 andfirst charge discharging unit 7 enter a conductive state. Thus,electrons generated at the photoelectric conversion unit 8 may be movedto the first holding unit 10, and the electrons of the first holdingunit 10 are discharged to the OFD area 112. At this time, it isdesirable that a potential barrier at the first charge discharging unit7 is lower than the potential of the photoelectric conversion unit 8.According to such a potential state, electrons generated at thephotoelectric conversion unit 8 may be moved to the OFD area 112. Inthis manner, when the second holding unit 12 holds electrons, the chargeof the first holding unit 10 is discharged to the OFD area 112. That isto say, the first holding unit 10 may be reset.

FIG. 8A illustrates potential states of the pixels at the second rowduring a period from the point-in-time tAcc to the point-in-time t19.Specifically, this indicates a state in which when the second holdingunit 12 holds electrons, an accumulation period starts. The first chargetransfer unit 9 and first charge discharging unit 7 enter anon-conductive state. Therefore, electrons generated at thephotoelectric conversion unit 8 are accumulated at the photoelectricconversion unit 8 and first holding unit 10.

FIG. 8B illustrates potential states of the pixels at the second rowduring a period from the point-in-time t19 to the point-in-time t20. Thethird charge transfer unit 13 enters a conductive state. Thus, electronsheld at the second holding unit 12 is transferred to the input node 14of the amplifier unit 15. In order to improve the transfer efficiency ofelectrons from the second holding unit 12, it is desirable that theheight of a potential barrier at the time of conduction of the thirdcharge transfer unit 13 is lower than the height of potential of thesecond holding unit 12. Further, it is desirable that the height ofpotential of the input node 14 of the amplifier unit 15 is lower thanthe height of potential of the second holding unit 12.

FIG. 8C illustrates potential states of the pixels at the second rowduring a period from the point-in-time t20 to the point-in-time t23.This is a diagram illustrating potential states after the third chargetransfer unit 13 enters a non-conductive state.

Note that, with the potentials of the pixels at the first row during aperiod from the point-in-time t11 to the point-in-time t12, asillustrated in FIG. 7D, when the first charge transfer unit 9 and firstcharge discharging unit 7 are in a conductive state, the third chargetransfer unit 13 enters a conductive state. Thus, though light is inputto the photoelectric conversion unit 8, electrons are discharged fromthe first charge discharging unit 7 to the OFD area 112. On the otherhand, the electrons of the second holding unit 12 are transferred to theinput node 14 of the amplifier unit 15. In order to improve the transferefficiency of electrons from the second holding unit 12, it is desirablethat the height of a potential barrier at the time of conduction of thethird charge transfer unit 13 is lower than the height of potential ofthe second holding unit 12. Further, it is desirable that the height ofpotential of the input node 14 of the amplifier unit 15 is lower thanthe height of potential of the second holding unit 12.

The potentials of the pixels at the first row during a period from thepoint-in-time t12 to the point-in-time t15 are in a state in whichelectrons are held at the input node 14 of the amplifier unit 15 in thepotential states illustrated in FIG. 7D. At the point-in-time t15, uponthe input nodes 14 of the amplifier units 15 of the pixels at the firstrow being reset, charge held at the input nodes 14 of the amplifierunits 15 are discharged.

With some embodiments, the potential of the first holding unit 10 islower than the potential of the photoelectric conversion unit 8. Asillustrated in FIG. 6A, when the first charge transfer unit 9 is in anon-conductive state, and as illustrated in FIG. 6D, when the firstcharge transfer unit 9 is in a conductive state, in either case, thepotential of the first holding unit 10 is lower than the potential ofthe photoelectric conversion unit 8. With such a configuration, theelectrons of the first holding unit 10 are readily discharged by thefirst charge discharging unit 7 being connected to the first holdingunit 10. This is because the potential of the photoelectric conversionunit 8 is higher, and accordingly, it is difficult to discharge theelectrons of the first holding unit 10 via the photoelectric conversionunit 8.

With some embodiments, the first charge discharging unit 7 may beconnected to the photoelectric conversion unit 8. In this case, when thefirst charge transfer unit 9 is in a conductive state, the potential ofthe first holding unit 10 becomes higher than the potential of thephotoelectric conversion unit 8, and accordingly, the charge of thefirst holding unit 10 may be discharged. Such a potential state may beformed with a relation between the impurity concentration of asemiconductor region which makes up the first holding unit 10 and theimpurity concentration of a semiconductor region which makes up thephotoelectric conversion unit 8. Alternatively, the above-mentionedpotential state may be formed by voltage to be applied to the controlelectrode of the first holding unit 10. It is desirable that the controlelectrode of the first charge transfer unit 9 and the control electrodeof the first holding unit 10 is electrically separated. Thus, thepotential of the first charge transfer unit 9 and the potential of thefirst holding unit 10 may independently be controlled. Therefore, it iseasy to increase the potential of the first holding unit 10 as comparedto the photoelectric conversion unit 8.

Also, with some embodiments, as illustrated in FIG. 7B, when the secondcharge transfer unit 11 is in a conductive state, the potential of thesecond holding unit 12 is lower than the potential of the first holdingunit 10. According to such a potential state, transfer of charge fromthe first holding unit 10 to the second holding unit 12 may effectivelybe performed. Alternatively, according to such a potential state,complete depletion transfer from the first holding unit 10 to the secondholding unit 12 is enabled. The complete depletion transfer is thatcharge is transferred by the entirety of the N-type semiconductor region103 which makes up the first holding unit 10 being depleted.

With a configuration wherein when the second charge transfer unit 11 isin a conductive state, the potential of the second holding unit 12 islower than the potential of the first holding unit 10, it is desirableto connect a reset unit to the input nodes 14 of the amplifier units 15.Thus, the electrons of the second holding unit 12 may be discharged viathe input node 14 of the amplifier 15. That is to say, the secondholding unit 12 may be reset via the input node 14 of the amplifier unit15. This is because the potential of the first holding unit 10 ishigher, and accordingly, it is difficult to discharge the electrons ofthe second holding unit 12 via the first holding unit 10.

Also, with the second holding unit 12, a period to hold electrons maydiffer depending on rows. Therefore, when noise caused at the secondholding unit 12 is great, this causes shading, and accordingly, theimage quality may deteriorate. On the other hand, noise caused at thesecond holding unit 12 may be reduced by reducing the number of channelsto be connected to the second holding unit 12. The channels are chargetransfer paths of which the potentials are controlled. Specifically, itis desirable that the number of channels to be connected to the secondholding unit 12 is two. One is a charge transfer path from the firstholding unit 10 to the second holding unit 12. The other is a chargetransfer path from the second holding unit 12 to the input node 14. Notethat there may be another path where charge overflowing from the secondholding unit 12 moves.

As described above, with some embodiments, the charge of the firstholding unit 10 may be discharged. According to such a configuration,the image quality of an image pickup apparatus may be improved.

Second Embodiment

Another embodiment of the image pickup apparatus according to thepresent technology will be described. The present embodiment differsfrom the first embodiment in that the present embodiment includes asecond charge discharging unit 29 which is connected to thephotoelectric conversion unit 8. Therefore, with the present embodiment,only points different from the first embodiment will be described, anddescription will be omitted regarding the other portions.

The overall block configuration of the image pickup apparatus accordingto the present embodiment is the same as with the first embodiment.Specifically, FIG. 1 is an overall block diagram of the image pickupapparatus according to the present embodiment.

FIG. 9 illustrates an equivalent circuit of the image pickup apparatusaccording to the first embodiment. Portions having the same functions aswith FIG. 2 are denoted with the same reference numerals as with FIG. 2,and accordingly, detailed description will be omitted. Here, though 6pixels in a total of two rows by three columns are illustrated, an imagepickup area may be configured by an even greater number of pixels beingdisposed.

With some embodiments, pixels include the second charge discharging unit29. The second charge discharging unit 29 transfers electrons from thephotoelectric conversion unit 8 to a second OFD area. The second OFDarea is a charge discharging node that discharges charges. The secondOFD area may include, for example, an N-type semiconductor region thatis connected electrically to a wiring 28 which supplies power supplyvoltage. The second charge discharging unit 29 may be configured toinclude a control electrode disposed on the semiconductor substrate viathe insulating film. With some embodiments, electronic shutter operationmay be performed with the second charge discharging unit 29. That is tosay, a period to discharge electrons generated at the photoelectricconversion unit 8 (shutter period) and a period to accumulate electrons(exposure period) may be controlled by controlling the second chargedischarging unit 29.

A fifth transfer control wiring 27 supplies a driving pulse PTX4 to acontrol electrode that configures the second charge discharging unit 29(hereinafter, fifth control gate). The height of the potential barrierof the semiconductor region below the fifth control gate may be changedby changing a pulse value to be supplied to the fifth control gate. Thatis to say, the charge transfer path disposed under the control electrodemay be controlled by the second charge discharging unit 29. With someembodiments, portions of other pixels are the same as with the firstembodiment.

With some embodiments, the pixel configuration illustrated with theequivalent circuit exemplified in FIG. 9, the electrical path betweenthe photoelectric conversion unit 8 and the first holding unit 10 mayhave the following configuration. The configuration thereof is aconfiguration wherein the first charge transfer unit 9 disposed in theelectrical path between the photoelectric conversion unit 8 and thefirst holding unit 10 is in a non-conductive state, and electrons areallowed to be moved from the photoelectric conversion unit 8 to thefirst holding unit 10. Here, the non-conductive state is a state inwhich of pulse values to be supplied to the first charge transfer unit9, a pulse value to generate the highest potential barrier has beensupplied. Accordingly, the first charge transfer unit 9 does not have tobe so-called completely off, and the non-conductive state of the firstcharge transfer unit 9 also includes a state in which some sort ofpotential barrier has occurred as compared to a case where the firstcharge transfer unit 9 has completely been turned on.

For example, in the event that a MOS transistor is used as the firstcharge transfer unit 9, a specific configuration may be made by this MOStransistor having an embedded channel configuration. More generallyspeaking, this configuration is a configuration wherein there is aportion in an area deeper than the surface where the potential barrierfor electrons is lower than the surface when the first charge transferunit 9 is in a non-conductive state. In this case, a driving pulse to besupplied to the first charge transfer unit 9 may be a fixed value. Thatis to say, s fixed potential barrier may be employed instead of aconfiguration wherein two states of a conductive state and anon-conductive state are switchable.

According to such a configuration, when light is input to thephotoelectric conversion unit 8, most of the electrons generated byphotoelectric conversion are moved to the first holding unit 10 duringthe exposure period. Accordingly, the accumulation periods of all of thepixels disposed in the image pickup area 2 may be aligned.

Further, when the first charge transfer unit 9 is in a non-conductivestate, a hole is accumulated on the surface. Also, the channel whereelectrons move exists in a predetermined depth portion from the surface,and accordingly, influence of dark current may be reduced as compared toa case where electrons move in an interface between the semiconductorsubstrate and the insulating film.

Alternatively, the electrical path between the photoelectric conversionunit 8 and the first holding unit 10 may have another configuration. Theother configuration is a configuration wherein the first charge transferunit 9 disposed in the electrical path between the photoelectricconversion unit 8 and the first holding unit 10 is in a non-conductivestate, and no electrons are moved from the photoelectric conversion unit8 to the first holding unit 10. Here, the non-conductive state is astate in which of pulse values to be supplied to the first chargetransfer unit 9, a pulse value to generate the highest potential barrierhas been supplied. In other words, this is a configuration wherein themajority of electrons generated by photoelectric conversion areaccumulated in the photoelectric conversion unit 8.

During a period for accumulating electrons at the photoelectricconversion unit 8, a lower potential barrier than the potential barrierat the first charge transfer unit 9 is formed, and accordingly, aconfiguration wherein no electrons are moved from the photoelectricconversion unit 8 to the first holding unit 10 may be obtained. As for aspecific configuration, when the first charge transfer unit 9 and thesecond charge transfer unit 29 are in a non-conductive state, apotential barrier to be formed below the first control gate is higherthan a potential barrier to be formed below the fifth control gate. Notethat, when the first charge transfer unit 9 and second chargedischarging unit 7 are in a non-conductive state, electrons may beaccumulated at the photoelectric conversion unit 8.

According to such a configuration, the majority of electrons generatedby photoelectric conversion at the time of light being input to thephotoelectric conversion unit 8 are transferred to the first holdingunit 10 during the exposure period. Accordingly, with all of the pixelsdisposed in the image pickup area 2, by the transfer of chargesaccumulated in the photoelectric conversion unit 8 to the first holdingunit 10, the accumulation periods of all of the pixels may be aligned.

Specific configurations of pixels of some embodiments will be describedwith reference to FIGS. 10 and 11. Portions having the same functions aswith FIGS. 3 and 4 are denoted with the same reference numerals. Theportions denoted with the same reference numerals as with FIGS. 3 and 4are the same as with the first embodiment, and accordingly, detaileddescription will be omitted.

FIG. 10 illustrates a top view of image pickup apparatuses according tosome embodiments. Here, though six pixels in a total of two rows bythree columns are illustrated, an image pickup area may be configured byan even greater of pixels being disposed.

Pixels 100 each include a control electrode 201 which configures thesecond charge discharging unit 29, and a second OFD area 202. The otherportions are the same as with the first embodiment. Further, the secondOFD area 202 may be shared with the source or drain of the resettransistor, the selecting transistor, or the amplifier transistor. Thatis to say, the charge of the photoelectric conversion unit 8 istransferred to the source or drain of one of the reset transistor, theselecting transistor, and the amplifier transistor. According to such aconfiguration, the area of the photoelectric conversion unit 8 may beincreased, and accordingly, sensitivity may be improved.

The second charge discharging unit 29 may be configured with a MOStransistor configured with a control electrode 201, an N-typesemiconductor region 101, and a second OFD area 202. The controlelectrode 201 included in the second charge discharging unit 29 isdisposed adjacent to the N-type semiconductor 101 on a parallel line.According to such a configuration, the second charge discharging unit 29may discharge charges from the photoelectric conversion unit 8.

FIG. 11A is a schematic view illustrating a cross section along the lineXIA-XIA. The same reference numerals are used for portions having thesame functions as in FIG. 4A. FIG. 11B is a schematic view illustratingthe cross section along the line XIB-XIB from FIG. 10. FIG. 11B is thesame figure as FIG. 4B. That is to say, the cross section along the lineXIB-XIB of the embodiment is the same as the cross section long the lineIVB-IVB in the first embodiment.

As illustrated in FIG. 11A, with some embodiments, electrons generatedat the photoelectric conversion unit 8 have a potential to be dischargedin the second OFD area 202 through a channel 308 disposed under thecontrol electrode 201. The second OFD area is connected to a plug notdepicted in the diagram. The second OFD area 202 connects to a wiring 28though the plug. The plug is configured from a metal such as tungsten.Further, other portions of FIG. 11A are the same as in the firstembodiment.

Next, a driving method according to some embodiments will be described.FIG. 12 illustrates a driving pulse diagram of the image pickupapparatus according to some embodiments. This is a pulse diagramillustrating a case of performing global electronic shutter operationwherein exposure periods agree regarding all of the pixels disposed inthe image pickup area 2. The numbers in parenthesis indicate the numberof rows, and in the present drawing, driving pulses to be supplied tothe pixels in the first and second rows are illustrated. PSEL indicatesa driving pulse to be supplied to the gate of the selecting transistor.PRES indicates a driving pulse to be supplied to the gate of the resettransistor. PTX1 indicates a driving pulse to be supplied to the firstcontrol gate. PTX2 indicates a driving pulse to be supplied to thesecond control gate. PTX3 indicates a driving pulse to be supplied tothe third control gate. PTX4 indicates a driving pulse to be supplied tothe fifth control gate. PMRES1 indicates a driving pulse to be suppliedto the fourth control gate. PTS indicates a driving pulse for performingsample hold of a light signal using, for example, the memory unitdisposed in the column circuit. PTN indicates a driving pulse forperforming sample hold of noise signal using, for example, the memoryunit disposed in the column circuits. All of the driving pulses are in ahigh level at the time of a conductive state.

At point-in-time t1 and theretofore, the PRES in all of the rows in theimage pickup area 2 is in a high level. For this reason, the voltage ofthe input node for amplifier unit 15 is reset. Here, all other pulsesdepicted in FIG. 5 are in a low level. For this reason, electronsgenerated by photoelectric conversion at the photoelectric conversionunit 8 are accumulated. That is to say, the exposure period has startedbefore the point-in-time t1. During exposure periods, of electronsgenerated at the photoelectric conversion unit 8, a predetermined amountof electrons may move to the first holding unit 10. During exposureperiods, all charges may be accumulated in the photoelectric conversionunit 8.

At the point-in-time t1, in a state which the PRES maintains a highlevel, with all of the pixels disposed in the image pickup area 2, thePTX3 makes the transition from a low level to a high level. Thus, thesecond holding unit 12 is reset. That is to say, the charge in thesecond holding unit 12 is discharged through a resetting unit 17. At thepoint-in-time t2, with all of the pixels disposed in the image pickuparea 2, the PTX3 makes the transition from a high level to a low level.Thus, the second holding unit 12 is reset.

Also, with some embodiments, at the point-in-time t1, all of the pixelsdisposed in the image pickup area 2, the PMRES1 makes the transitionfrom a low level to a high level. Thus, the first charge dischargingunit 7 becomes conductive, and the electrons in the first holding unit10 are discharged through the OFD area 112. That is to say, the firstholding unit 10 resets. After this, at the point-in-time t2, with allthe pixels disposed in the image pickup area 2, PMRES1 makes thetransition from a high level to a low level. Thus, the first holdingunit is reset. In this way, with some embodiments, before electronstransfer to the first holding unit 10, the first holding unit 10 isreset.

After elapsing of a predetermined period following the point-in-time 2,at point-in-time 3, the PTX1 in all of the rows in the image pickup area2 makes the transition from a low level to a high level, and atpoint-in-time t4, the PTX1 in all of the rows in the image pickup area 2makes the transition from a high level to a low level. According to thisoperation, the electrons remaining in the photoelectric conversion unit8 are transferred to the first holding unit 10. According to thisoperation, the exposure periods are ended.

At a point-in-time tsh, PTX4 makes the transition from a low level to ahigh level. Thus, the second charge discharging unit 29 changes to aconductive state. For this reason, the electrons generated byphotoelectric conversion at the photoelectric conversion unit 8 aredischarged through the second OFD area 202. In this way, with someembodiments, the state when the second charge discharging unit 29 isconductive is the shutter period. Further, at the point-in-time tsh, thefirst holding unit 10 is holding electrons.

At the point-in-time t5, the PTX2 in all of the rows in the image pickuparea 2 makes the transition from a low level to a high level, and at thepoint-in-time t6, the PTX2 in all of the rows in the image pickup area 2makes the transition from a high level to a low level. According to thisoperation, the electrons held in the first holding unit 10 aretransferred to the second holding unit 12.

At the point-in-time t7, the PMRES1 in all of the rows disposed in theimage pickup apparatus makes the transition from a low level to a highlevel. Thus, the first charge discharging unit 7 is conductive, and sothe electrons in the first holding unit 10 are transferred to the OFDarea 112. In this way, with some embodiments, during the period from thepoint-in-time t7 to the point-in-time tAcc, the first charge dischargingunit 7 and the second charge discharging unit 29 are both conductive.

At the point-in-time t8, the PSEL (1) makes the transition from a lowlevel to a high level. According to this operation, the signal of thepixel in the first row changes to a state where it may be output by avertical signal line 20. Further, at the point-in-time t8, the PRES (1)makes the transition from a high level to a low level. Thus, the resetoperation of the input node 14 in the amplifier unit 15 completes.

At the point-in-time t9, the PTN makes the transition from a low levelto a high level, and at the point-in-time t10, the PTN makes thetransition from a high level to a low level. According to thisoperation, a noise signal is held at, for example, the memory unit fornoise signals disposed in the column circuit.

At the point-in-time t11, the PTX3 (1) makes the transition from a lowlevel to a high level, and at the point-in-time t12, the PTX3 (1) makesthe transition from a high level to a low level. According to thisoperation, the electrons held by the second holding unit 12 for thepixel in the first row are transferred to the input node 14 in theamplifier unit 15.

At the point-in-time t13, the PTS makes the transition from a low levelto a high level, and at the point-in-time t14, the PTS makes thetransition from a high level to a low level. According to thisoperation, a light signal on which a noise signal is superimposed isheld at, for example, the memory unit for light signals disposed in thecolumn circuit.

At the point-in-time t15, the PSEL (1) makes the transition from a highlevel to a low level. According to this operation, the readout period ofthe signal for the pixel in the first row ends. The period of the signalfor the pixel in the first row is the period from the point-in-time t8to the point-in-time t15. Further, at the point-in-time t15, the PRES(1) makes the transition from a low level to a high level. Thus, theresetting of the input node 14 in the amplifier unit 15 for the pixel inthe first row is started.

After this, from the point-in-time t16 to the point-in-time 23, thereadout of the signal for the pixel in the second row is performed. Thisoperation is the same as that of the first row, and so the descriptionof which will be omitted. Besides the difference that the drivingpulses, which are the high levels, correspond to the second row, theoperations that occur at each point-in-time from the point-in-time t16to the point-in-time t23 are the same as those that occur during eachpoint-in-time from the point-in-time t8 to the point-in-time t15.

Here, at the point-in-time tAcc between the point-in-time t15 and thepoint-in-time t16, the PTX4 in all of the rows disposed in the imagepickup apparatus and the PMRES1 make the transition from a high level toa low level. Thus, electrons generated by photoelectric conversion areheld in the photoelectric conversion unit 8 and the first holding unit.That is to say, the exposure period is started.

With some embodiments, until the exposure period at the point-in-timetAcc starts, PMRES1 is at a high level. That is to say, before theexposure period starts, the electrons in the first holding unit 10 aredischarged through the OFD area 112. Preferably, before the exposureperiod starts, the electrons remaining in the first holding unit 10 aredischarged. Accordingly, when starting accumulation of the electrons inthe first holding unit 10, the electrons holding in the first holdingunit 10 may be decreased, or completely removed.

Conversely, at the point-in-time tAcc, the second charge dischargingunit 12 for the pixel in the second row holds electrons. With someembodiments, according to the disposition of the first chargedischarging unit 7 which discharges the electrons in the first holdingunit 10, the electrons in the first holding unit 10 may be dischargedwhen the second holding unit 12 holds the electrons.

Further, with some embodiments, only the second charge discharging unit29 may be in a non-conductive state at the point-in-time tAcc. Accordingto such an operation, while the electrons in the first holding unit 10are discharging, the electrons generated by photoelectric conversion mayaccumulate in the photoelectric conversion unit 8. In this case, beforethe electrons in the photoelectric conversion unit 8 are transferred tothe first holding unit 10, the PMRES1 makes the transition to the highlevel.

Further, FIG. 5 illustrates an example of the exposure period startingbetween the point-in-time t15 and the point-in-time t16. However, thepoint-in-time tAcc which starts the exposure period is not limited tothis case. The point-in-time tAcc which starts the exposure period canexist at any time after the point-in-time t6 which is when electrons aretransferred from the first holding unit 10.

According to such an operation, the exposure periods may be equalizedregarding all of the pixels disposed in the image pickup area 2. Thisoperation is performed at the entire image pickup surface at the sametime until the transfer to the first holding unit 12. The specificpoint-in-time thereof is the point-in-time t6. Thereafter, readout ofall of the rows in the image pickup area 2 is performed by repeating thereadout operation.

With some embodiments, enabling the first charge discharging unit 7 andthe second charge discharging unit 29 to drive independently improvesthe degree of freedom for the driving of the image capture apparatus.For example, the first charge discharging unit 9 ends the exposureperiod by transferring the electrons in the photoelectric conversionunit 8 to the first holding unit 10, and the second charge dischargingunit 29 becomes conductive before the second charge transfer unit 11transfers electrons to the first holding unit 10. According to such anoperation, electrons generated at the photoelectric conversion unit 8are not mixed, and discharged through the second OFD area 202. Theresult is a decrease in noise.

Also with some embodiments, electrons in the first holding unit 10 aredischarged by the first charge discharging unit 7, and electrons in thephotoelectric conversion unit 8 are discharged by the second chargedischarging unit 29. Thus, regardless of the state of any of thepotential of the photoelectric conversion unit 8, the potential of thefirst holding unit 10, and the potential of the first charge transferunit 9 between both of these, electrons generated during the shutterperiod may be discharged. The result is a decrease in noise.

Next, the relationship between potentials with some embodiments will bedescribed. FIGS. 13 through 15 illustrate a relation of height of apotential barrier at each point-in-time and period in the pulse drivingdiagram illustrated in FIG. 12. FIGS. 13 through 15 illustrate thepotentials of the photoelectric conversion unit 8, the first chargetransfer unit 9, the first holding unit 10, the second charge transferunit 11, the second holding unit 12, the third charge transfer unit 13,the input node 14 in the amplifier unit 15 (FD area 107), the firstcharge discharging unit 7, the OFD area 112, the second chargedischarging unit 29, and the second OFD area 202. The potential ofpixels for some embodiments are illustrated with a solid line.Potentials are positional energy of signal charges. In FIGS. 13 through15, the lower part of the diagrams represent signal charges with a lowpotential, and the upper part of the diagrams represent signal chargeswith a high potential.

FIG. 13A illustrates the potential state before the point-in-time t1.The first charge transfer unit 9, the second charge transfer unit 11,the third charge transfer unit 13, the first charge discharging unit 7,and the second charge discharging unit 9 are in a non-conductive state.Thus, the potential barrier generated by the first charge transfer unit9 and the first charge discharging unit 7 is high. As a result, thecharge generated by photoelectric conversion is held in thephotoelectric conversion unit 8.

With some embodiments, at this time, the potential of the second chargedischarging unit 29 and the first charge transfer unit 9 have nearly thesame height. The potential of the second charge discharging unit 29 maybe lower than the potential of the first charge transfer unit 9.Alternatively, the potential of the second charge discharging unit 29may be higher than the potential of the first charge transfer unit 9. Ifthe height of the two potentials is different, and electrons over apredetermined amount are generated by the photoelectric conversion unit8, the electrons will transfer through the channel with the lowerpotential.

Also with some embodiments, regarding this state, the potential of thephotoelectric conversion unit 8, the potential of the first holding unit10, and the potential of the second holding unit 12 are all nearly thesame. These potentials may have different heights.

FIG. 13B illustrates the potential state during the period from thepoint-in-time t1 to the point-in-time t2. As described in FIG. 12, forthe period from the point-in-time t1 to the point-in-time t2, a highlevel pulse is supplied to the third charge transfer unit 13. That is tosay, the potential barrier generated at the third charge transfer unit13 is in a low state. Thus, the electrons in the second holding unit 12are discharged through the drain of the reset transistor (not depictedin the diagram). It is preferable that electrons do not exist in thesecond holding unit 12. Also, a high level pulse is supplied to thefirst charge discharging unit 7. That is to say, the potential barriergenerated at the first charge discharging unit 7 is in a low state.Thus, the electrons in the first holding unit 10 are discharged throughthe OFD area 112. It is preferable that electrons do not exist in thefirst holding unit 10.

FIG. 13C illustrates the potential state during the period from thepoint-in-time t2 to the point-in-time t3. The third charge transfer unit13 and the first charge discharging unit 7 are non-conductive, and sothe potential barriers of the third charge transfer unit 13 and thefirst charge discharging unit 7 are high. This state is the same as thatof FIG. 13A.

FIG. 13D illustrates the potential state during the period from thepoint-in-time t3 to the point-in-time t4. At this time, the first chargetransfer unit is in a conductive state. Thus, the electrons accumulatedin the photoelectric conversion unit 8 are transferred to the firstholding unit 10. To increase the transfer efficiency of electrons fromthe photoelectric conversion unit 8, it is preferable if the potentialbarrier at the time when the first charge transfer unit 9 is conductiveis lower than the potential of the photoelectric conversion unit 8.Further, it is preferable if the potential of the first holding unit 10is lower than the potential of the photoelectric conversion unit 8.

With some embodiments, the control electrode 102 is shared by the firstcharge transfer unit 9 and the first holding unit 10. Thus, when thedriving pulse is supplied to the first charge transfer unit 9, thepotential of the first holding unit 10 lowers. Therefore, as illustratedin FIG. 13A, the potential when there are no electrons in thephotoelectric conversion unit 8 may either the same as the potential ofthe first holding unit 10, or may be lower.

FIG. 14A illustrates the potential state during the period from thepoint-in-time t4 to the point-in-time tsh. This state illustrated isafter the first charge transfer unit 9 changes to a non-conductivestate, and before the second charge transfer unit 11 changes to aconductive state. Also, the first charge discharging unit 7 is in anon-conductive state. Thus, the amount of electrons accumulated in thefirst holding unit 10 is determined by the potential barrier generatedby the first charge transfer unit 9 and the first charge dischargingunit 7.

FIG. 14B illustrates the potential state during the period from thepoint-in-time tsh to the point-in-time t5. The second charge dischargingunit 29 is in a conductive state. That is to say, the potential barrierof the second charge discharging unit 29 is in a low state. It ispreferable that the potential of the second charge discharging unit 29is lower than the potential of the photoelectric conversion unit 8. As aresult, the charge generated by the photoelectric conversion unit 8 isdischarged.

FIG. 14C illustrates the potential state during the period from thepoint-in-time t5 to the point-in-time t6. The second charge transferunit 11 is in a conductive state. Thus, the electrons held in the firstholding unit 10 are transferred to the second holding unit 12 throughthe second transfer unit 11. To increase the transfer efficiency ofelectrons from the first holding unit 10, it is preferable if thepotential barrier at the time when the second charge transfer unit 11 isconductive is lower than the potential of the first holding unit 10.Further, the potential of the second holding unit 12 is preferably lowerthan the potential of the first holding unit 10.

With some embodiments, the control electrode 104 is shared with thesecond charge transfer unit 11 and the second holding unit 12. Thus,when a driving pulse is supplied to the second charge transfer unit 11,the potential of the second charge transfer unit 11 lowers, and thepotential of the second holding unit 12 also lowers. Therefore, asillustrated in FIG. 13A, when all charge transfer units are in anon-conductive state, the potential of the first holding unit 10 may bethe same as the potential of the second holding unit 12.

FIG. 14D illustrates the potential state during the period from thepoint-in-time t6 to the point-in-time t7. Both the second chargetransfer unit 11 and the third charge transfer unit 13 are in anon-conductive state, and electrons are accumulated in the secondholding unit 12 via their potential barriers.

When the first charge discharging unit 7 is in a conductive state at thepoint-in-time t7, the potential barrier of the first charge dischargingunit 7 in FIG. 14D lowers. Thus, the electrons in the first holding unit10 are discharged through the OFD area 112.

FIG. 15A illustrates the potential state when the first chargedischarging unit 7 and the second charge discharging unit 29 are in anon-conductive state, at the point-in-time tAcc. Further, FIG. 15Aillustrates the potential state of pixels in the second row that haveaccumulated a charge at the second holding unit 12 at this time. Asillustrated in FIG. 15A, the exposure period may start while electronsare held at the second holding unit 12.

FIG. 15B illustrates the potential state of pixels in the second rowduring the period from the point-in-time t19 to the point-in-time t20.Electrons in the second holding unit 12 are transferred to the inputnode 14 in the amplifier unit 15. FIG. 15C illustrates the potentialstate of pixels in the second row during the period from thepoint-in-time t20 to the point-in-time t22. The third charge transferunit 13 is in a non-conductive state.

Further, the potentials of the photoelectric conversion unit 8, thefirst charge transfer unit 9, the first holding unit 10, the secondcharge transfer unit 11, the second holding unit 12, the third chargetransfer unit 13, the input node 14 in the amplifier unit 15, the firstcharge discharging unit 7, and the OFD area 112 may be the same as thoseof the first embodiment.

With some embodiments, when the first charge transfer unit 9 asillustrated in FIG. 13D is in a conductive state, the potential of thefirst holding unit 10 is lower than the potential of the photoelectricconversion unit 8. According to such a configuration, by connecting thefirst charge discharging unit to the first holding unit 10, electrons inthe first holding unit 10 discharge more easily. As the potential of thephotoelectric conversion unit 8 is higher, it is difficult for electronsin the first holding unit 10 to discharge through the photoelectricconversion unit 8.

Further, with some embodiments, the first charge discharging unit 7 maybe omitted. In this case, when the first charge transfer unit 9 is in aconductive state, the potential of the first holding unit 10 is higherthan the potential of the photoelectric conversion unit 8, and soelectrons in the first holding unit 10 are discharged.

Regarding pixels omitted by the first charge discharging unit 7 in FIG.16, this illustrates the potential state when the first holding unit 10is reset. The potential of the first charge transfer unit 9 is lowerthan the potential of the first holding unit 10. The potential of thephotoelectric conversion unit 8 is lower than the potential of the firstcharge transfer unit 9. Also, the potential of the second chargedischarging unit 29 is lower than the potential of the photoelectricconversion unit 8. As a result, the electrons in the first holding unit10 are discharged through the second OFD area 202.

Such a potential state may be formed by the relationship between theimpurity concentration of the semiconductor region that configures thefirst holding unit 10 and the semiconductor region that configures thephotoelectric conversion unit 8. Alternatively, the previously describedpotential state may be formed by a voltage applied to the controlelectrode of the first holding unit 10. At this time, the controlelectrode of the first charge transfer unit 9 and the control electrodeof the first holding unit 10 may be electrically separated. As a result,the potential of the first charge transfer unit 9 and the potential ofthe first holding unit 10 may be controlled independently. Thus, thepotential of the first holding unit 10 may easily be made higher thanthat of the photoelectric conversion unit 8.

Also, with some embodiments, as illustrated in FIG. 14C, when the secondcharge transfer unit 11 is in a conductive state, the potential of thesecond holding unit 12 is lower than the potential of the first holdingunit 10. According to such a potential state, the transfer of chargesfrom the first holding unit 10 to the second holding unit 12 may beperformed efficiently. Alternatively, according to such a potentialstate, it is possible to have a complete transfer depletion from thefirst holding unit 10 to the second holding unit 12. Complete transferdepletion is the transfer of a charge by the depletion of the entireN-type semiconductor region 103, which configures the first holding unit10.

When the second charge transfer unit 11 is in a conductive state, andwith a configuration where the potential of the second holding unit 12is lower than the potential of the first holding unit 10, it ispreferable to connect the reset unit to the input node 14 in theamplifier unit 15. Thus, electrons in the second holding unit 12 may bedischarged through the input node 14 in the amplifier unit 15. That isto say, the second holding unit 12 may be reset through the input node14 in the amplifier unit 15. As the potential of the first holding unit10 is higher, it is difficult for electrons in the second holding unit12 to discharge through the first holding unit 10.

Also, the period that electrons are held by the second holding unit 12may differ for each row. Thus, if there is a large amount of noisegenerated from the second holding unit 12, there is a potential thatimage quality will decrease due to shading. In response to this, bydecreasing the number of channels connected to the second holding unit,noise generated by the second holding unit 12 may be decreased. Channelsare charge transfer paths controlled by the potential. Specifically, itis preferable that the number of channels connected to the secondholding unit 12 be two. One is the charge transfer path from the firstholding unit 10 to the second holding unit 12. The other is the chargetransfer path from the holding unit 12 to the input node 14. Further,there may be other paths for the transfer of charges that overflow fromthe second holding unit 12.

As described above, with some embodiments, electrons in the firstholding unit 10 may be discharged. Such a configuration enables animprovement in image quality of the image pickup apparatus.

Third Embodiment

Another embodiment of the image pickup apparatus will be described. Thefollowing some embodiments differ from the second embodiment in that athird charge discharging unit 30 connected to the second holding unit 12is provided. The other portions are all the same as with the firstembodiment or second embodiment. Therefore, with the following someembodiments, only points different from the first and second embodimentswill be described, and description will be omitted regarding the otherportions.

The overall block configurations of the image pickup apparatusesaccording to the following some embodiments is the same as with thefirst embodiment or second embodiment. Specifically, FIG. 1 is anoverall block diagram of the image pickup apparatuses according to thefollowing some embodiments.

FIG. 17 illustrates an equivalent circuit of image pickup apparatusesaccording to some embodiments. Portions having the same functions aswith FIG. 2 or 9 are denoted with the same reference numerals as withFIG. 2 or 9, and detailed description will be omitted. Here, though sixpixels in a total of two rows by three columns are illustrated, an imagepickup area may be configured by an even greater number of pixels beingdisposed.

With some embodiments, the pixels include a third charge dischargingunit 30. The third charge discharging unit 30 transfers the electrons ofthe second holding unit 12 to the OFD area. The OFD area is a chargedischarging node from which charge is discharged. The OFD area may beconfigured of an N-type semiconductor region electrically connected to awiring 31 which supplies power supply voltage, for example. The thirdcharge discharging unit 30 may be configured to include a controlelectrode disposed on the semiconductor substrate via the insulatingfilm.

A sixth transfer control wiring 32 supplies a driving pulse PMRES2 tothe control electrode (hereinafter, the sixth control gate) which makesup the third charge discharging unit 30. The height of a potentialbarrier of a semiconductor region below a sixth control gate may bechanged with a pulse value to be supplied to the sixth control a gate.That is to say, the third charge discharging unit 30 may controlpotential of a charge transfer path to be disposed below the controlelectrode. The other portions of the pixels according to someembodiments are all the same as with the first embodiment.

With some embodiments, at the pixel configuration illustrated with theequivalent circuit exemplified in FIG. 17, the electrical path betweenthe photoelectric conversion unit 8 and the first holding unit 10 mayhave the following configuration. The configuration thereof is aconfiguration wherein the first charge transfer unit 9 disposed in theelectrical path between the photoelectric conversion unit 8 and thefirst holding unit 10 is in a non-conductive state, and electrons areallowed to be moved from the photoelectric conversion unit 8 to thefirst holding unit 10. Here, the non-conductive state is a state inwhich of pulse values to be supplied to the first charge transfer unit9, a pulse value to generate the highest potential barrier has beensupplied. Accordingly, the first charge transfer unit 9 does not have tobe so-called completely off, and the non-conductive state of the firstcharge transfer unit 9 also includes a state in which some sort ofpotential barrier has occurred as compared to a case where the firstcharge transfer unit 9 has completely been turned on.

For example, in the event that a MOS transistor is the first chargetransfer unit 9, a specific configuration may be realized by this MOStransistor having an embedded channel configuration. More generallyspeaking, this configuration is a configuration wherein there is aportion in an area deeper than the surface where the potential barrierfor an electrode is lower than the surface when the first chargetransfer unit 9 is in a non-conductive state. In this case, a drivingpulse to be supplied to the first charge transfer unit 9 may be a fixedvalue. That is to say, fixed potential barrier may be employed insteadof a configuration wherein two states of a conductive state and anon-conductive state are switchable.

According to such a configuration, when light is input to thephotoelectric conversion unit 8, almost of electrons generated byphotoelectric conversion are moved to the first holding unit 10 duringthe exposure period. Accordingly, the accumulation periods of all of thepixels disposed in the image pickup area 2 may be aligned by performingtransfer of charge from the first holding unit 10 to the second holdingunit 12 in parallel.

Further, when the first charge transfer unit 9 is in a non-conductivestate, a hole is accumulated on the surface. Also, the channel whereelectrons move exists in a predetermined depth portion from the surface,and accordingly, influence of dark current may be reduced as compared toa case where electrons move in an interface between the semiconductorsubstrate and the insulating film.

Alternatively, the electrical path between the photoelectric conversionunit 8 and the first holding unit 10 may have another configuration. Theother configuration is a configuration wherein the first charge transferunit 9 disposed in the electrical path between the photoelectricconversion unit 8 and the first holding unit 10 is in a non-conductivestate, and no electrons are moved from the photoelectric conversion unit8 to the first holding unit 10. Here, the non-conductive state is astate in which of pulse values to be supplied to the first chargetransfer unit 9, a pulse value to generate the highest potential barrierhas been supplied. In other words, this is a configuration wherein themajority of electrons generated by photoelectric conversion isaccumulated in the photoelectric conversion unit 8.

During a period for accumulating electrons at the photoelectricconversion unit 8, a lower potential barrier than the potential barrierat the first charge transfer unit 9 is formed, and accordingly, aconfiguration wherein no electrons are moved from the photoelectricconversion unit 8 to the first holding unit 10 may be obtained. As for aspecific configuration, when the first charge transfer unit 9 and secondcharge discharging unit 29 are in a non-conductive state, a potentialbarrier to be formed below the first control gate is higher than apotential barrier to be formed below the fifth control gate. Note that,when the first charge transfer unit 9 and second charge discharging unit7 are in a non-conductive state, electrons may be accumulated at thephotoelectric conversion unit 8.

According to such a configuration, the majority of electrons generatedby photoelectric conversion at the time of light being input to thephotoelectric conversion unit 8 is accumulated in the photoelectricconversion unit 8 during the exposure period. Accordingly, with all ofthe pixels disposed in the image pickup area 2, charge accumulated inthe photoelectric conversion units 8 is simultaneously transferred tothe first holding units 10, whereby the accumulation periods of all ofthe pixels may be aligned.

A specific configuration of pixels according to some embodiments will bedescribed with reference to FIG. 18. Portions having the same functionas with FIG. 3 or 10 are denoted with the same reference numerals.Portions denoted with the same reference numerals as with FIG. 3 or 10are the same as with the first or second embodiment, and accordingly,detailed description will be omitted.

FIG. 18 illustrates a top view of the image pickup apparatuses accordingto some embodiments. Here, though six pixels in a total of two rows bythree columns are illustrated, an image pickup area may be configured byan even greater number of pixels being disposed.

The pixels 100 include a control electrode 203 which makes up the thirdcharge discharging unit 30. The other portions thereof are the same aswith the first embodiment. Note that the charge discharging node of thethird charge discharging unit 30 is the OFD area which is common to thecharge discharging node of the first charge discharging unit 7 (controlelectrode 111) of an adjacent pixel. The present is not restricted tothis, and the charge discharging node of the first charge dischargingunit 7 and the charge discharging node of the third charge dischargingunit 30 may be different semiconductor regions. Also, the chargedischarging node of the third charge discharging unit 30 may be sharedwith the source or drain of the reset transistor, selecting transistor,or amplifier transistor.

The control electrode 203 included in the third charge discharging unit30 is disposed adjacent to the N-type semiconductor region 105 with aplanar view. According to such displacement, the third chargedischarging unit 30 may discharge the charge of the second holding unit12. The third charge discharging unit 30 may be a MOS transistorconfigured of the control electrode 203, N-type semiconductor region105, and OFD area 112.

A cross-sectional configuration according to some embodiments may be thesame as with the first embodiment or second embodiment. Also, a drivingmethod according to some embodiments may be the same as with the firstembodiment or second embodiment. However, when resetting the secondholding unit 12, the third charge discharging unit 30 is electricallyconducted.

Fourth Embodiment

An embodiment of an image pickup system will be described. Examples ofthe image pickup system include digital still cameras, digital camcoders, duplicating machines, fax machines, cellular phones, in-vehiclecameras, and observation satellites. FIG. 19 illustrates a block diagramof a digital still camera as an example of the image pickup system.

In FIG. 19, reference numeral 1001 denotes a barrier for protecting alens, 1002 denotes a lens which causes an image pickup apparatus 1004 toform an optical image of a subject, and 1003 denotes an aperture forvarying the amount of light passed through the lens 1002. Referencenumeral 1004 denotes an image pickup apparatus described in theabove-mentioned embodiments, which converts an optical image formed bythe lens 1002 as image data. Now, let us say that an AD conversion unithas been formed on the semiconductor substrate of the image pickupapparatus 1004. Reference numeral 1007 denotes a signal processing unitwhich subjects image pickup data output from the image pickup apparatus1004 to various types of corrections, or compresses the data. In FIG.19, reference numeral 1008 denotes a timing generator which outputsvarious timing signals to the image pickup apparatus 1004 and signalprocessing unit 1007, and 1009 denotes an overall control unit whichcontrols the entire digital still camera. Reference numeral 1010 denotesa frame memory unit for temporarily storing image data, 1011 denotes aninterface unit for performing recording in or readout from a recordingmedium, and 1012 denotes a detachable recording medium such assemiconductor memory for recording or readout of image data. Referencenumeral 1013 denotes an interface unit for communicating with anexternal computer or the like. Here, a timing signal and so forth may beinput out of the image pickup system, and the image pickup system mayinclude at least the image pickup apparatus 1004 and the signalprocessing unit 1007 which processes an image pickup signal output fromthe image pickup apparatus 1004.

With some embodiments, the configuration has been described wherein theimage pickup apparatus 1004 and AD conversion unit are formed on thesame semiconductor substrate. However, the image pickup apparatus 1004and AD conversion unit may be provided to another semiconductorsubstrate. Also, the image pickup apparatus 1004 and signal processingunit 1007 may be formed on the same substrate.

As described above, the image pickup apparatus according to embodimentsmay be applied to the image pickup system. The image quality of theimage pickup system may be improved by applying the image pickupapparatus according to embodiments to the image pickup system.

While the disclosure has been described with reference to exemplaryembodiments, it is to be understood that the disclosure is not limitedto the disclosed exemplary embodiments. The scope of the followingclaims is to be accorded the broadest interpretation so as to encompassall such modifications and equivalent structures and functions.

This application claims the benefit of Japanese Patent Application No.2012-033356 filed Feb. 17, 2012, which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. An image pickup apparatus comprising: a pluralityof pixels, each of the plurality of pixels including a photoelectricconversion unit; a first holding unit configured to hold a chargegenerated by the photoelectric conversion unit, at a location differentfrom location of the photoelectric conversion unit; a second holdingunit configured to hold a charge held by the first holding unit at alocation different from locations of both of the first holding unit andthe photoelectric conversion; an amplifying unit including an input nodeand configured to output a signal based on a charge transferred to theinput node from the second holding unit, the input node being adifferent node from the second holding unit; a reset unit configured toreset a voltage of the input node; and a first discharge unit configuredto discharge a charge of the first holding unit, wherein the firstdischarge unit includes a charge draining node, wherein the chargedraining node is electrically connected to a line to which apredetermined voltage is to be supplied, wherein the first dischargeunit is configured to discharges a charge held by the first holding unitto the charge draining node, wherein the reset unit is configured todischarge a charge of the second holding unit via the input node, andwherein each of the plurality of pixels includes a third transfer unitconfigured to transfer a charge from the second holding unit to theinput node.
 2. The image pickup apparatus according to claim 1, whereina charge is transferred from the photoelectric conversion unit to thefirst holding unit via a first path; wherein a charge is transferredfrom the first holding unit to the second holding unit via a secondpath; and wherein the first discharge unit discharges the charge of thefirst holding unit via a third path which differs from both of the firstpath and the second path.
 3. The image pickup apparatus according toclaim 2, wherein each of the plurality of pixels includes a firsttransfer unit configured to transfer a charge from the photoelectricconversion unit to the first holding unit, and a second transfer unitconfigured to transfer a charge from the first holding unit to thesecond holding unit.
 4. The image pickup apparatus according to claim 1,wherein the first discharge unit is configured to discharge a charge ofthe photoelectric conversion unit via the first holding unit.
 5. Theimage pickup apparatus according to claim 1, wherein each of theplurality of pixels includes a second discharge unit configured todischarge a charge of the photoelectric conversion unit; wherein thesecond discharge unit includes a second charge draining node; whereinthe second charge draining node is electrically connected to a line towhich a predetermined voltage is to be supplied; and wherein the seconddischarge unit configured to discharge a charge of the photoelectricconversion unit to the charge draining node.
 6. The image pickupapparatus according to claim 1, further comprising a control unit;wherein the control unit is configured to control the first dischargeunit to discharge a charge of the first holding unit in parallel withholding, by the second holding unit, a charge thereof.
 7. An imagepickup system comprising: the image pickup apparatus according to claim1; and a signal processing unit which processes signals output from theimage pickup apparatus.
 8. An image pickup apparatus comprising: aplurality of pixels, each of the plurality of pixels including aphotoelectric conversion unit; a first holding unit configured to hold acharge generated by the photoelectric conversion unit, at a locationdifferent from location of the photoelectric conversion unit; a secondholding unit configured to hold a charge held by the first holding unitat a location different from locations of both of the first holding unitand the photoelectric conversion; an amplifying unit including an inputnode and configured to output a signal based on a charge transferred tothe input node from the second holding unit, the input node being adifferent node from the second holding unit; a reset unit configured toreset a voltage of the input node; and a first discharge unit configuredto discharge a charge of the first holding unit, wherein the firstdischarge unit includes a charge draining node, wherein the chargedraining node is electrically connected to a line to which apredetermined voltage is to be supplied, wherein the first dischargeunit is configured to discharges a charge held by the first holding unitto the charge draining node, wherein the reset unit is configured todischarge a charge of the second holding unit via the input node, andwherein the charge draining node is a node different from the inputnode.
 9. The image pickup apparatus according to claim 8, wherein acharge is transferred from the photoelectric conversion unit to thefirst holding unit via a first path; wherein a charge is transferredfrom the first holding unit to the second holding unit via a secondpath; and wherein the first discharge unit discharges the charge of thefirst holding unit via a third path which differs from both of the firstpath and the second path.
 10. The image pickup apparatus according toclaim 9, wherein each of the plurality of pixels includes a firsttransfer unit configured to transfer a charge from the photoelectricconversion unit to the first holding unit, and a second transfer unitconfigured to transfer a charge from the first holding unit to thesecond holding unit.
 11. The image pickup apparatus according to claim8, wherein the first discharge unit is configured to discharge a chargeof the photoelectric conversion unit via the first holding unit.
 12. Theimage pickup apparatus according to claim 8, wherein each of theplurality of pixels includes a second discharge unit configured todischarge a charge of the photoelectric conversion unit; wherein thesecond discharge unit includes a second charge draining node; whereinthe second charge draining node is electrically connected to a line towhich a predetermined voltage is to be supplied; and wherein the seconddischarge unit configured to discharge a charge of the photoelectricconversion unit to the charge draining node.
 13. The image pickupapparatus according to claim 8, wherein each of the plurality of pixelsincludes a third transfer unit configured to transfer a charge from thesecond holding unit to the input node.
 14. The image pickup apparatusaccording to claim 8, further comprising a control unit; wherein thecontrol unit is configured to control the first discharge unit todischarge a charge of the first holding unit in parallel with holding,by the second holding unit, a charge thereof.
 15. An image pickup systemcomprising: the image pickup apparatus according to claim 8; and asignal processing unit which processes signals output from the imagepickup apparatus.